1. Field of the Invention
The present invention relates to a injection molded article used with photosensitive material, for example, a photo film cartridge, a photo sheet film case, a lens-fitted film unit, a container for photo film cassette, a photo film spool, a photo film cassette made of resin (a cassette for so-called advanced photo system and so on), an instant film unit, an instant film pack, a cartridge for photo disc film, a winding spool, a cassette shell, a core for film-like photosensitive material, a sheet film pack and a sheet film unit.
2. Description of the Related Art
Conventionally, injection molded articles used with photosensitive material, for example, 135-type photo film spool, a core for film-like photosensitive material, a lens-fitted film unit in which a photo film is built beforehand, and a photo film cassette made of resin (for Advanced Photo System, hereinafter, APS), are molded by injection with various resin compositions in order to improve light shielding property, impact resistance, abrasion resistance and so forth.
Japanese Utility Model Publication No. 61-36995 discloses that a photo film spool is made of polystyrene resin or impact resistance polystyrene resin. In this case, when a film end engages with a claw provided on the photo film spool, excellent engaging force of 11.3 Kg is obtained.
Japanese Utility Model Publication No. 2-37799 discloses that a core for film-like photosensitive material is molded by using impact resistance polystyrene resin including rubber-like material, and a gate position of which is restricted. In this case, generation of weld line is reduced and compression strength is improved. Further, injection molding property is improved because gate processing is not required.
Japanese Patent Laid-open publication No. 63-226643 discloses that a lens-fitted film unit is molded by using resin composition in which carbon black is added in impact resistance polystyrene resin of low melt flow index. In this case, necessary light shielding property is obtained.
Japanese Patent laid-open Publication No. 1-312538 discloses that an outer case of a photo film cassette (APS) is molded by resin composition in which carbon black is added to impact resistance polystyrene resin of low melt flow index. In this case, necessary light shielding property is obtained.
Resin composition having light shielding property for a lens-fitted film unit, a photo film cassette made of resin and so forth are disclosed in Japanese Patent Laid-open Publication No. 7-295150. In the resin composition, at least one kind of organic compound having number average molecular weight of less than 10,000 is 0.001-45 wt. %, at least two kinds of antioxidant are 0.002-1 wt. %, and at least one kind of thermoplastic having number average molecular weight of 10,000 or more is 50 wt. % or more.
However, when the photo film spool is molded with above-described resin composition, scatter due to molding tends to be generated and engaging force and physical strength are sometimes greatly different. Further, injection molding property, heat resistance, dimensional accuracy, slip property, antistatic and abrasion resistance are not sufficient and there arises a problem with respect to photographic property.
When a core for film-like photosensitive material is molded by injection with resin composition including rubber-like material or the like, a wound photosensitive material roll is hard to slip due to property of the rubber-like material so that good winding is obtained. However, friction force of the core surface becomes large so that injection molding property and abrasion resistance are not sufficient. Further, when the core surface becomes slippy due to lubricant, surfactant and so forth added thereto, winding property of the roll film becomes bad. It is hard to obtain good winding, injection molding property and abrasion resistance at the same time.
As to the above-described lens-fitted film unit, carbon black is added in conventional impact resistance polystyrene resin of low melt flow index so that it is necessary to increase the resin temperature because flowability of the resin decreases. Therefore, pyrolysis of the resin and the additive tends to be generated so that it is hard to obtain a good photographic property. Further, molding cycle is long and appearance is not good because many weld lines are generated. Moreover, physical strength is low. This is caused due to lack of consideration about the resin composition. Accordingly, further improvement of the resin is desired.
Due to the resin composition used for the photo film cassette, sufficient light shielding property is obtained. However, molding cycle is long and it is expensive. The improvement of slipping property, antistatic, photographic property, heat resistance, appearance and physical strength are desired to be improved. Moreover, many weld lines are generated.
On the other hand, due to the above-described conventional injection molding material, it is possible to reduce generation of micro grid and deterioration of photographic property. Further, generation of trouble due to burned resin is a little so that it is possible to perform successive molding. However, in order to obtain perfect light shielding by adding light shielding material of 2 wt. % or less, further improvement is desired. The light shielding material is fine particle and tends to cohere such as carbon black having a mean particle size of 100 m.mu. or less and oil absorption of 50 ml/100 g or more. Moreover, in order to improve the physical strength of injection molded article and to reduce the generation of weld lines, further improvement is desired.